any of various minerals consisting of hydrous silicates of aluminum or potassium etc. that crystallize in forms that allow perfect cleavage into very thin leaves; used as dielectrics because of their resistance to electricity
造句
用作名詞(n.)
They are mica which makes up the rest of the total rock. 這塊巖中余下的黑色礦物部分就是云母。
So the dark mica in this granite should be called biotite. 那么,在這塊花崗巖中的黑色云母類礦物就應當叫做黑云母了。